Beamforming and Interference alignment (IA) are techniques for interference suppression. Beamforming is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in the array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity. The improvement compared with omnidirectional reception/transmission is known as the receive/transmit gain (or loss).
Interference alignment (IA) for wireless networks is a technique for increasing the multiplexing gain on the interference channel. It consists in forcing interfering signals at each receiver into a reduced-dimensional subspace of the received space, so that the receivers can observe an interference-free desired signal. The considered space may be an actual space (time, frequency, physical path) or structural space of the signal.
Beamforming at transmitter needs to know downlink channel. This is normally done by a communication between the transmitter and receiver.
Additionally, Uplink-Downlink channels still require frequent calibration due to drift in front-end electronics. This required low-rate feedback of the CSI between TX/RX pairs. While it is possible to calibrate corresponding TX/RX pairs, it is not possible to calibrate crosslinks between interfering pairs that are not communicating pairs in an interference channel.